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Sunday, July 24, 2016

Gemstone Mining

Recently we took a day and went mining for gem stones.  In particular, we were after Star Garnets, the official state gemstone of Idaho.

Garnets are pretty common, and being fairly hard stones, they are frequently used as abrasives.  Garnet hardness is about 7.5 on a scale of 1-10, with talc being a 1 and diamond being a 10

Below:  A roll of garnet sandpaper.  Garnet for modern abrasives is now manufactured rather than mined.

Most people don't know about Star Garnet.  The Star Garnet is a rare type of garnet with an impurity in the form of rutile needles that create a star image in the gemstone.  It takes a very skilled gemstone cutter to produce a stone with a nicely centered star.

Below:  A cut and polished star garnet.

Star Garnets are not seen in retail jewelry.  Most of the cut stones are found in private collections or have been mounted in custom jewelry by their owner.

Star Garnets are found in just a handful of places in the world.  Of those places, only Idaho allows the public an opportunity to dig them up - so off we went for a day of hard work and getting dirty!

The place where the Star Garnets are located is named after another gemstone.  It is called Emerald Creek (Below).

There is a small mining/sorting facility near this creek for visitors.  The forest service brings in a truckload of dirt every few years that is rich in star garnets.  It's the visitor's job to sift through the dirt for gravel, and then sift through the gravel for garnets.

It's a four step process:

  1. Fill a bucket with pay dirt
  2. Sift through dirt and mud to segregate out the stones (gravel).
  3. Rinse the mud and dirt off the gravel and segregate the garnets
  4. Throw the tailings (waste gravel) on the junk pile.  Repeat until you are out of energy.
We picked a great day, because it was very cool and overcast, but yet it did not rain.  Had it been hot or rainy, things would have ended pretty quickly.

Below is the dirt pile where you (hopefully) fill your bucket with lovely star garnets.

The next step is screening, where you get rid of about 90% of the material you just shoveled into the bucket!  Below is the screening area.  This is probably the most physical part of the operation.  You have to shake the screening box side to side pretty hard to knock the dirt out.  We had to deal with mud, which also clogged the screen, and had to be brushed out frequently.

The last step in getting your star garnet is washing away the dirt.  For this, they set up long sluice boxes to wash dirt from a lot of visitor's screening boxes at once.

At the end of it all, you end up with a lot of wet gravel, and a few (sometimes none) star garnets.

Below is our 12 ounce pile of stones that we collected out of 10 buckets of dirt from the pile:

My daughter also pulled out a pretty cool rock that has a bunch of small garnets embedded in a mica-schist stone, below:

Most importantly we got outdoors, had a great time and saw some beautiful country along the way.

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